1. Field
One embodiment of the invention relates to a fuel cell device.
2. Description of the Related Art
Nowadays, secondary batteries such as lithium ion batteries have been commonly used as a power supply for electronic devices such as portable notebook computers and mobile devices.
Recent improvement in the performance of such electronic devices increases their power consumption and creates the demand to prolong their use time. In view of this, fuel cells with high output that do not need recharging and are small in size are expected as a new power supply. Among the fuel cells is a direct methanol fuel cell (DMFC) which uses an aqueous methanol solution circulated therein. Methanol as a fuel in the DMFC is easy to handle compared to hydrogen used as a fuel for other types of fuel cells. Further, the DMFC has a simple structure, and thus has attracted attention as a power supply for electronic devices.
A conventional DMFC includes a DMFC stack having a fuel electrode, an air electrode and an electrolyte membrane, a fuel supply path for supplying an aqueous methanol solution to the fuel electrode, and an air supply path for supplying air to the air electrode. The air supply path is provided with an air inlet for drawing in air from the surrounding atmosphere.
On the fuel electrode of the DMFC stack, methanol reacts with water and is oxidized, which generates hydrogen ions, carbon dioxide, and electrons. The hydrogen ions pass through the electrolyte membrane and reach the air electrode. On the air electrode, oxygen in the air combines with the hydrogen ions and the electrons, and thus is reduced to water. At this time, current flows through an external circuit connected between the fuel electrode and the air electrode, and electricity is generated.
If the air supplied to the DMFC stack contains, for example, hydrocarbon compounds, the compounds adhere to the air electrode. This poses an obstacle to the reduction reaction on the air electrode. Since a decrease in the reduction reaction lowers the electricity generation performance of the DMFC, hydrocarbon compounds need to be removed from the air when the DMFC takes in oxygen for the reduction reaction from the air.
For example, Japanese Patent Application Publication (KOKAI) Nos. 2001-185193 and 2007-188640 each disclose a conventional DMFC including an air intake filter. The air intake filter is arranged on the air supply path extending from the air inlet to the air electrode, and cleans air drawn in through the air inlet. That is, the air intake filter has a function of absorbing hydrocarbon compounds.
To maintain the original electricity generation performance of the DMFC, the cleaning performance of the air intake filter needs to be maintained at a high level. Therefore, it is desirable that the air intake filter be replaced frequently to prevent its cleaning performance from degrading.